Efforts are being made for the technological development of semiconductor devices that satisfy various required specifications according to their applications. In devices having an insulating film structure on a semiconductor substrate, there exist requirements for an improved quality of the insulating film, which will enhance their basic performances.
For example, semiconductor devices that are formed on a silicon (Si) substrate, which are generally used for LSIs, have attained higher degrees of integration through miniaturization, whereby their performances have been drastically enhanced. Conventionally, a very high quality thermally-grown oxide film (thermal SiO2 film) is used as a gate insulating film thereof, and miniaturization has been made possible through the film becoming thinner, etc. Recent years have met with limitations for the thermal SiO2 film to become any thinner, and for further miniaturization, high-k dielectric insulating films or the like are being introduced.
On the other hand, wide-band gap semiconductors are drawing attention as semiconductor materials for power devices which have a high breakdown voltage and in which a large current can flow. For example, silicon carbide (SIC) has a particularly high breakdown field, and therefore is expected as a semiconductor which is optimum for a next generation of low-loss power devices.
On SiC, an SiO2 film with a relatively good quality can be formed through thermal oxidation. However, its MIS interface will contain defects associated with many thermal SiO2 films, e.g., interface state, and the very low channel mobility of MIS transistors and difficulties to attain reliability have presented a problem. On the other hand, reports have been made in the recent years that, after a thermal oxide film is formed or an SiO2 film is formed via CVD, a nitriding treatment step may be introduced to dope the SiO2/SiC interface with a high concentration of nitrogen, thus reducing the interface state and improving the channel mobility.
For example, Patent Document 1 discloses a production method which involves a step of performing a nitriding treatment for an SiC surface in an ambient that contains an NO gas or N2O gas, and, following the nitriding treatment step, a step of performing film formation on the SiC surface by a chemical or physical vapor phase epitaxy technique.
An MIS interface that involves a gate insulating film which is formed through any such process is proven to have a reduced interface state and a considerably improved channel mobility.